A bit error rate (“BER”) is a ratio of bits received, processed, and/or transmitted with errors to a total number of bits received, processed, and/or transmitted over a given period of time. A BER is typically expressed as ten to a negative power. If, for example, a transmission comprises 1 million bits and one of these bits is in error (e.g., a bit is a first logic state instead of a second logic state), the transmission has a BER of 10−6. The BER is useful because it may characterize the ability of a device to receive, process, and/or transmit bits.
Many devices are designed to receive, process, and then transmit a plurality of bits. An optoelectronic transceiver, for example, typically receives a plurality of bits in an electrical form and then transforms and transmits the bits in an optical form and/or receives a plurality of bits in an optical form and then transforms and transmits the bits in an electrical form.
To derive a BER for a device under test (“DUT”), bits transmitted to the DUT are compared to corresponding bits transmitted by the DUT or to corresponding bits in a pattern used to generate the bits transmitted to the DUT. In some applications, the BER of a DUT must be below a defined threshold for the DUT to pass a test.
A Bit Error Rate Test or Tester (“BERT”) is a procedure or device that establishes a BER for a DUT or to otherwise quantify a DUT's ability to receive, process, and/or transmit bits. More specifically, a BERT measures the BER of a transmission (e.g., bits transmitted, received, or processed) over a given period of time by a DUT. An exemplary BERT includes, among other components, a serializer/deserializer (“SERDES”) and a clock source fixed to a host board (e.g., PCB, circuit board, etc.). Typically, the SERDES produces serial encoded data (e.g., the bits) used to establish a BER for a DUT. More specifically, serial encoded data is transmitted from a SERDES to a DUT, which attempts to transmit the serial encoded data back to the SERDES. The SERDES compares the output of the DUT to the input to the DUT (or what the input should have been).
In prior art BERTs, however, only one BER is established for a DUT. More specifically, electrical data generated by the BERT is sent to the electrical input terminal of the DUT. This data is converted and transmitted through an optical output terminal of the DUT. But this optical output terminal is connected to optical input terminal of the DUT so that optical data transmitted by the DUT is looped back to the same DUT. Once this optical data is received by the DUT, is converted and transmitted through an electrical output terminal to the BERT. As a result, the source of bit errors that occur during such testing can not be attributed to a specific data path through the DUT. One data path starts at the electrical input terminal of the DUT and ends at the optical output terminal of the DUT. The other data path starts at the optical input terminal of the DUT and ends at the electrical output terminal of the DUT.